I'm rooting for something like this too. As for the carbonfact and their focus on promoting eco brands, I'd like them to present an alternative metric if/when possible.
Measuring each individual product is complicated and doesn't have to reflect brand's entire emission output. If a company is 10% manufacturing and 90% marketing then the methodology used by carbonfact will be underreporting the emissions.
Some brands (inc. Nike) are already disclosing their total emission. Others might be forced to do so in a near future by regulators. Would it be possible to have a metric calculated simply as 'total emissions / units sold'?
